The present invention relates generally to electronically controlled internal combustion engines and, more particularly, to a method and system of throttle control calibration.
Increasingly, internal combustion engines are equipped with electronic control units (ECU) that dynamically control engine and engine component operation based on sensory feedback received from the engine and its components. From the feedback, the ECU, which typically includes one or more microprocessors and electronic maps, is able to assess such parameters as throttle position and air intake to control fuel injection and ignition systems, among other engine systems, to optimize engine performance. In this regard, the ECU is able to control the engine to operate with improved fuel efficiency and reduced emissions.
ECU control of the engine and its components is commonly governed, to an extent, on feedback received from a throttle position sensor (TPS). A TPS is commonly used to provide feedback to the ECU as to the relative position of a throttle actuator or lever between an idle position and a wide open throttle (WOT) position. As is well-known, the throttle actuator is linked by a throttle linkage to a throttle plate which is caused to rotate relative to an air intake opening by a throttle shaft positioned in a throttle body so as to control air intake to the engine. Typically, the throttle plate is caused to rotate in response to operator-initiated commands that are received across the throttle linkage. The throttle linkage customarily connects the throttle shaft to the throttle actuator, e.g. foot pedal or hand controlled device. In marine applications, the throttle actuator may typically be found as a hand controlled device at the bridge or control station of a watercraft.
Ideally, a single throttle linkage would be used to connect the throttle shaft (and ultimately the throttle plate) to the throttle actuator. With a single piece throttle linkage, a more accurate or precise measurement of throttle actuator and throttle plate position is obtainable. That is, with a throttle linkage that includes multiple throttle pieces or components, the TPS may not output an accurate throttle actuator position as a result of variances, play, or slop in the linkage. This can be particularly problematic for marine applications such as outboard motors.
It is not uncommon for outboard motors to be sold independent of a watercraft. That is, a consumer may already own or has selected to purchase a watercraft and desires to replace an existing motor or have a motor added, respectively. As such, watercraft are typically constructed to have a throttle actuator linkage that is to be connected to a separate throttle linkage of the outboard motor when the motor is mounted to the watercraft. Therefore, multiple linkages or components are used to connect the throttle assembly of the motor to the throttle actuator assembly of the watercraft. These multiple linkages create response variances that can negatively affect the precision of a TPS output.
For example, when an operator “pulls back” on the throttle actuator in an open throttle position, the combined throttle linkages will cause the throttle shaft to rotate the throttle plate to a more closed position. As the throttle is moved to a more closed position, air intake is reduced. Feedback regarding this more-toward-closed action is received by the ECU from the TPS whereupon the ECU may command the fuel injection and ignition systems to adjust their operation in light of the reduced air intake and lower desired speed. When a watercraft operator pulls completely back on the throttle actuator, or indicates by other means, a desire to bring the engine to idle, the throttle linkage ideally induces movement of the throttle shaft to rotate the throttle plate to a fully closed position. Idle is typically defined as the engine's slowest practical operating speed. Driving the engine to idle typically results in a rotation of the throttle plate to a closed position. Typically, either the throttle plate is left open a small amount at idle for air entry, or holes are provided in the throttle plate to provide a passage of air to the engine when the throttle plate is closed. That is, there in a range of engine operation that may be defined between engine idle and engine operation when the throttle plate is closed.
As a result of the variances in the throttle linkage connecting the throttle plate to the throttle actuator, the throttle actuator may reach an idle indicative position, but the throttle linkage may not. Accordingly, the ECU will adjust subsequent engine operations on a perceived but not actual idle throttle position. Specifically, idle throttle positioning is deemed to occur when the throttle actuator is within a range of throttle actuator positions independent of actual throttle plate or throttle shaft position. Moreover, the ECU will also adjust subsequent engine operation when a WOT position is detected within a pre-set range. Just as the variances in the throttle linkages affect the determination of idle, the variances also affect the determination of WOT.
At WOT, some ECUs may ignore the oxygen sensor signal in the engine's exhaust system and drive the fuel injection system to provide a rich fuel mixture for combustion. Accordingly, it is paramount that the ECU accurately determine, based on TPS output, when the throttle actuator is at idle or at WOT. The TPS is typically a potentiometer that includes a rotating lever or wiper arm that moves across a resistive element and outputs a different voltage value in response. For example, at WOT, the TPS may output a five volt signal. At idle, the TPS may output a 0.5 volt signal. The wiper arm, which rotates as a function of the throttle linkage, is typically constructed to have a rotating range that exceeds the rotating range of the throttle plate. In this regard, the wiper arm may continue to rotate to a more WOT position, but the throttle plate will not open any further and the TPS will not provide a different output signal than that achieved at WOT. The same, however, is not true at idle.
While a fully open throttle plate is indicative of WOT, a closed throttle plate is not indicative of idle engine running. As mentioned above, throttle plates may include one or more holes that allow the passage air to the engine when the plate is closed. Accordingly, the wiper arm will continue to rotate even though the throttle plate has closed. This additional rotation is necessary to indicate to the ECU that the throttle actuator has been driven to a position beyond that defined by throttle plate closing. As such, when the TPS provides an output of 0.5 volts, the throttle actuator is deemed to be at a position corresponding to engine idle. However, as noted above, as a result of variances in the throttle linkage, the TPS may not be able to provide 0.5 volt output even though the throttle actuator is at a position corresponding to engine idle. Conversely, the TPS may not be able to provide a 5.0 volt output even though the throttle actuator is at a position corresponding to WOT or provide a 5.0 volt output even though the throttle plate has not reached a WOT position. As a result, the ECU may not optimize subsequent engine operation.
One solution that has been developed is to define a range of positions in which the throttle actuator may be positioned to be indicative of desired engine idle. In this regard, if the TPS provides an output within a certain range, the ECU will deem the throttle actuator to be at a corresponding idle position and control subsequent engine operation accordingly. This solution similarly provides a range of acceptable WOT values such that if the TPS provides an output within this range, the ECU will control the engine and its components to run according to WOT.
One drawback of this solution is its complexity. Another is the manner in which it is applied. Regarding the former, idle and WOT ranges must be defined and separately monitored which greatly adds to the micro-processing power needed of the ECU as well as its memory requirements. Regarding the latter, this solution redefines a TPS idle and a TPS WOT output only at each engine startup. That is, a maximum and a minimum value for output of the TPS is determined at engine startup and is stored, provided the values fall within a pre-defined range. For the remainder of the engine operating session, these values will be used to define when the throttle actuator has reached a position corresponding to engine-at-idle or engine-at-WOT. Since a percentage opening of the throttle plate will govern engine operation, actual throttle actuator position relative to the minimum (idle) and maximum (WOT) values will be controlling. While this may be appropriate for throttle actuator positions between idle and WOT, variances in the throttle linkages may prevent the TPS from outputting the minimum or maximum value or falsely provide a minimum or maximum output. Accordingly, the ECU will not deem the throttle actuator to be at a position corresponding to engine idle or WOT despite the appropriate positioning of the throttle actuator by the watercraft operator. Moreover, since the TPS measures a relative position of the throttle actuator rather than the actual throttle plate or throttle shaft position, the TPS may provide a false indication of WOT or idle position.
It would therefore be desirable to have a simplified system and method of calibrating an ECU for subsequent engine operation that accounts for variances in throttle linkages for optimized engine operation. It would also be desirable to have a TPS that provides an accurate measure of throttle plate as well as throttle actuator position for calibration of the ECU. It would be further desirable to have a system that recalibrates the ECU for subsequent engine operation when the throttle actuator is positioned at a position corresponding to idle independent of engine operating mode.